Past the Universe

I've always wondered about space. How it can go on forever. The only thing that ever truly goes on forever is numbers. You just add one. The question is, how do we know we can add one onto the length of the universe? Something has to be bigger than the universe. I know it. I've got this theory about it, too. Think of it this way;

I am sitting in a room, that room is inside a house. That house is in a neighborhood. The neighborhood is in a town. The town is in a city. That city is in a county. The county is in a state. This state is in a country. The county is in a continent. The continent is on the world. The world is in a solar system and the solar system is in a galaxy. That galaxy is in a universe.

Here's the question, what's the universe inside of?

Is that why we believe the universe goes on forever? Because we can't figure out what it's inside of? Sure we don't have the technology to get past the universe yet, but when we do, what will be there?

This small idea of whats past the universe brings me more ideas. What if one day we do go past the universe? We go past the stars and the galaxies. Will we really find something that amazes us, or will we be unsatisfied with the result? Are we surrounded by the so called 'black holes'? Is the universe slowly getting smaller as we speak? But we can only ask questions for now. Maybe we'll never find out. Some things are meant to be left alone. I think the universe is one of them.